The present invention relates to a method and apparatus to test the integrity of a filter which can be newly installed or which has been in service for some period of time.
Traditionally, the integrity of a filter is tested by injecting a volatile chemical vapor into an air inlet line of the filter for a short period of time while simultaneously measuring a chemical vapor concentration in a filter effluent. Freon-type chemicals (inert, halogenated vapors) are typically used for this purpose because they are weakly adsorbed and such chemicals can be detected at very low concentrations (parts per trillion) using an electron capture detector. However, a major problem occurs when the filter has been exposed to a high relative humidity (i.e., above about 70%). When an inlet air stream of the filter has a high relative humidity, some of the injected Freon will not be adequately adsorbed due to the fact that the adsorbed water in the filter greatly decreases the adsorption capacity of the Freon. Therefore, the Freon will be nearly immediately detected in the filter effluent thus producing a false leak signal.
To solve the above problems, it would be desirable to use a chemical that is water soluble (i.e., a hydrophilic chemical) rather than water insoluble Freon gases. The adsorption capacity of a water-soluble vapor, such as an acetone, is typically enhanced by the presence of adsorbed water. A chemical detection method would be desirable in which an output air stream of the filter is sampled, enriched, separated, and detected in a series of detection operation steps. Such a chemical detection method could increase the detection concentration sensitivity by a factor of about five hundred. This is important because the higher the detection limit, the more chemical is needed in the feed to measure a leak. For example, to test a small leak (effluent-to-feed concentration level smaller than 1.0×10−5) in a 20,000 CFM filter, the amount of the chemical needed would be reduced from about 30 kilograms to just 60 grams.
Accordingly, it has been considered desirable to develop an improved apparatus and method for testing integrity of a filter which is fully automated and easy to operate and would overcome the foregoing difficulties and others while providing better and more advantageous overall results.